Field of the Invention
The present invention relates in general to the field of information handling system circuit boards, and more particularly to blind via printed circuit board fabrication supporting press fit connectors.
Description of the Related Art
As the value and use of information continues to increase, individuals and businesses seek additional ways to process and store information. One option available to users is information handling systems. An information handling system generally processes, compiles, stores, and/or communicates information or data for business, personal, or other purposes thereby allowing users to take advantage of the value of the information. Because technology and information handling needs and requirements vary between different users or applications, information handling systems may also vary regarding what information is handled, how the information is handled, how much information is processed, stored, or communicated, and how quickly and efficiently the information may be processed, stored, or communicated. The variations in information handling systems allow for information handling systems to be general or configured for a specific user or specific use such as financial transaction processing, airline reservations, enterprise data storage, or global communications. In addition, information handling systems may include a variety of hardware and software components that may be configured to process, store, and communicate information and may include one or more computer systems, data storage systems, and networking systems.
Server information handling systems often include a number of storage devices to store information, such as hard disk drives. For example, a server rack supports multiple server information handling systems disposed in multiple slots and interfaced with each other by a switch. Each of the server information handling systems in the rack has a printed circuit board (PCB) that interfaces components of the server information handling system, such as one more processors each disposed in a socket, random access memory, a chipset with BIOS and similar firmware, one or more network interface cards (NIC), a baseboard management controller (BMC) and one or more hard disk drives. By directly connecting hard disk drives to a server information handling system, access is provided to information stored at local hard disk drives in a rapid manner as compared with retrieval of information through the switch. For example, Serial attached SCSI (SAS) hard disk drive connectors at a PCB provide information transfer rates of 6 Gb/s with planned transfer rates of 12 Gb/s.
Server information handling systems that include storage devices typically have a mid-plane circuit board assembly for connectivity in an enclosure, such as a rack slot. Generally, when a server information handling system's primary function is service of storage requests, the hard disk drives or other persistent storage devices are placed at the front portion of the chassis that holds the server information handling system in the rack to provide ease of access in the event that a storage device needs replacement. One typical goal is for the front portion of the server information handling system mid-plane circuit board to have 100% utilization for supporting storage devices with a maximum storage device connector density and the rear portion of the mid-plane circuit board having an interface to the storage controllers. For instance, SAS surface mounted connectors extend outwards from the upper surface of the mid-plane circuit board to interface with storage devices and press fit connectors extend outwards from the lower surface of the mid-plane circuit board to interface with storage controllers. Press fit connectors provide high speed backplane connections with very high pin counts to interface with multiple storage devices through circuit board connections with multiple surface mounted connectors.
One difficulty with upper and lower surface connector configurations is that press fit connectors are inserted into relatively large through hole vias in the mid-plane circuit board. Due to the large pin count of the press fit connectors, large sections of the mid-plane circuit board have through holes formed to accept connectors of the connector pin fields. SAS surface mount connectors located on the upper surface often coincide with the location of press fit connectors on the bottom surface. In order to co-locate storage device and press fit connectors, two mid-plane circuit boards are assembled in a sandwich configuration so that one mid-plane circuit board accepts the press fit connectors and the other mid-plane circuit board accepts the storage device surface mounted connectors. The two separate mid-plane circuit boards are then connected to each other with another set of press fit backplane connectors that avoid co-location with the first set of press fit connectors and the storage device surface mounted connectors. However, including a second set of press fit connectors to interface the two mid-plane circuit boards increases the cost of the system and introduces signal integrity issues that further increase manufacture costs. For example, back-drilling of press fit connectors vias eliminates stubs from assembly but increase manufacture steps and cost.